Cracks in a concrete driveway or path are a common headache for NZ homeowners — and if left untreated, they can let in water, worsen over winter frosts, and become a trip hazard. The good news is that many cracks are straightforward to repair yourself with the right products and a bit of preparation. Here's how to assess the damage and get the job done properly.
Step 1: Assess the Crack Before You Start
Not all cracks are equal. Before reaching for the filler, take a close look at what you're dealing with:
- Hairline cracks (under 1–2 mm wide): Usually surface-level shrinkage cracks from the original pour or seasonal movement. Generally cosmetic and easy to DIY.
- Moderate cracks (2–10 mm wide): May have been caused by tree roots, ground movement, or heavy vehicle loads. Worth filling, but investigate the cause first.
- Wide or deep cracks (over 10 mm), heaving, or sunken sections: These suggest underlying ground movement or structural failure. A professional assessment is recommended.
Also check whether the crack edges are level with each other. If one side is higher than the other (differential movement), this points to a deeper problem that filler alone won't solve.
Step 2: Gather Your Tools and Materials
For most DIY crack repairs you'll need:
- Concrete crack filler or repair mortar — products from Sika (such as their polyurethane sealants) or Ardex are widely available at NZ hardware stores
- Cold chisel and hammer (for undercutting wider cracks)
- Wire brush and stiff broom
- Angle grinder or oscillating tool (optional, for cleaning crack edges)
- Vacuum or compressed air
- Bonding primer (recommended for deeper repairs)
- Pointing trowel or putty knife
- Safety glasses and gloves
You'll find a good range of repair products at Bunnings or Mitre 10. Always read the product data sheet — NZ weather conditions (humidity, temperature) affect cure times.
Step 3: Prepare the Crack Properly
Good preparation is the difference between a repair that lasts and one that falls out in six months.
- Clean out the crack — remove all loose concrete, dirt, moss, and weeds. A wire brush and vacuum work well. For wider cracks, use a cold chisel to undercut the edges slightly (making the crack wider at the base than the surface) so the filler has something to grip.
- Wash and dry — rinse with water and allow to dry fully. Avoid repairing in wet or very cold conditions (below around 10°C).
- Apply bonding primer — for repairs deeper than about 10 mm, a bonding agent helps the new material adhere to the old concrete. Follow the manufacturer's instructions.
Step 4: Choose the Right Repair Product
| Crack Type | Recommended Product | Notes |
|---|---|---|
| Hairline (under 2 mm) | Concrete crack sealant / liquid filler | Easy to apply, flexible |
| Moderate (2–10 mm) | Polyurethane sealant or repair mortar | Good flexibility and adhesion |
| Wide / deep (10 mm+) | Hydraulic cement or structural repair mortar | May need backer rod first |
| Moving / expansion joints | Flexible polyurethane or silicone sealant | Must remain flexible |
For cracks in expansion joints, always use a flexible sealant — rigid filler will just crack again as the concrete moves with temperature changes, which is very common in NZ's variable climate.
Step 5: Apply the Repair
- For liquid fillers and sealants: Pour or inject into the crack, working from one end to the other. Smooth off with a putty knife or gloved finger.
- For repair mortars: Mix according to instructions, pack firmly into the crack in layers if deep, and trowel smooth. Feather the edges so there's no lip to catch on.
- Cure properly: Keep the repair damp for the first day or two if using a cementitious mortar (cover with damp hessian or plastic). Keep foot traffic off for at least 24 hours and vehicles off for several days — check the product instructions.
Step 6: Seal the Surface (Optional but Recommended)
Once the repair has fully cured, consider applying a concrete sealer over the whole driveway or path. This protects against water ingress, UV damage, and oil stains — all common issues in NZ conditions. BRANZ research highlights that moisture penetration is a leading cause of concrete deterioration in NZ, so sealing is a worthwhile investment.
When to Call a Professional
Some situations are best left to a qualified concreter:
- Cracks wider than 10 mm or with differential movement between edges
- Large sections of sunken, heaving, or crumbling concrete
- Cracks that keep returning after repair
- Driveways subject to heavy vehicle loads (trucks, machinery)
- If you suspect the subbase has failed or there's a drainage issue underneath
A professional concreter can assess whether a patch repair is sufficient or whether a section needs to be broken out and re-poured. For significant work, make sure your concreter is experienced and check references. You can find qualified local concreters on tradedirectory.co.nz.
Note: Concrete work on driveways and paths is generally not restricted work under NZ law, so homeowners can DIY. However, if your driveway repair involves any drainage connections or changes to stormwater, that work must be carried out by a licensed drainlayer — check the Plumbers Gasfitters & Drainlayers Board for licensed practitioners.
Safety Tips
- Wear safety glasses when chiselling or grinding — concrete chips can cause serious eye injury
- Wear gloves — cement-based products are alkaline and can irritate or burn skin
- If using an angle grinder, use appropriate hearing and respiratory protection
- Check WorkSafe NZ guidance on working safely with concrete and silica dust